Process for coloring anodic coatings on aluminum and aluminum alloys with metal salts

ABSTRACT

Colored coatings are produced by first subjecting an aluminum or its alloys to anodic oxidation in an electrolyte containing mainly sulfuric acid, by supplying an electric current comprising a direct current component and an alternating current component with the alternating current component at least as large as the direct current component, dipping the oxide coating in an aqueous solution containing metallic cations or anions without supplying the electric current and then subjecting the coating to sealing treatment to produce coloring thereof.

United States Patent Miyakawa et al.

1 May 9,1972

[54] PROCESS FOR COLORING ANODIC COATINGS ON ALUMINUM AND ALUMINUM ALLOYS WITH METAL SALTS [72] Inventors: Tldnhlto Miylkawa, No. 159, 2-chome,

I-Iorinouchi-machi; Kazuko Nngal, No. 11, I-Iinogaoka, Noba-machi, both of Minamiku, Yokohama City, Japan [22] Filed: Sept. 5, I969 [2]] Appl. No.: 855,769

Related U.S. Application Data [63] Continuation-impart of Ser. No. 586,980, Oct. 17,

I966, abandoned.

[52] U.S. CI. ..204/35 N, 204/38 A, 204/58 [5 l] Int. Cl. ..C23l 5/02 [58] Field oiSearch.. .....204/35.l, 38.l,58,DIG. 8, 204/33 [56] References Cited UNITED STATES PATENTS 2,987,417 6/l96l Cochran ..204/38.l

3,152,97010/1964 Jensen ..204/38.l 2,901,412 8/1959 Mostovychetal ..204/58 FOREIGN PATENTS OR APPLICATIONS 716,554 10/1954 GreatBritain ..204/58 Primary Examiner-John I-I. Mack Assistant Examiner-W. 1. Solomon Attorney-Moonray Kojirna [57] ABSTRACT 4 Claims, No Drawings PROCESS FOR COLORING ANODIC COATINGS ON ALUMINUM AND ALUMINUM ALLOYS WITH METAL SALTS RELATED APPLICATIONS This is a continuation-impart application to Ser. No. 586,980 filed Oct. 17, 1966 now abandoned.

This invention relates to a process for coloring the surface of aluminum or aluminum alloys, and more particularly to such a process employing a variety of types of electrical currents and one or more metal salt solutions.

Aluminum and aluminum alloys having colored surfaces have recently come into extensive use, for example as automobile fixtures, building materials, appliances and the like. The coloring of the surfaces must be color fast, uniform and available in different colors in order to be of extensive use.

Different methods have been used up to this time, but these methods provide coloring of anodized surface of aluminum by the use of either a process for coloring by the use of organic dyestuff, or a process for inorganic coloring by use of a secondary electrolysis.

One known method is the Asada process relating to secondary electrolysis which is disclosed in US. Pat. No. 3,382,160. In this prior art process, the surface of the aluminum matrix is subjected to anodic oxidation in an acid liquor with a direct current. The coloring step is carried out in an aqueous solution containing an acid and metal salt by using an alternating current. As a result, the coloring material to be obtained is deposited as a hydroxide or oxide.

From the above description, it can be appreciated that the electrolysis of the Asada method comprises two steps, first, a primary electrolysis using only direct current in the anodic oxidation step, and second, a secondary electrolysis using only alternating current in the coloring step.

The foregoing and other previous methods of plating or coloring surfaces of aluminum and aluminum based alloys have been limited in their selection of colors, lack of uniformity of coloring, and have had problems with reliability and secondary electrolysis.

An object of this invention is to provide a new, simple, and inexpensive process for coloring surfaces of aluminum or aluminum based alloys, which are color fast and stable.

We have discovered a new process which solves the foregoing problems and eliminates the foregoing and other disadvantages of prior art methods. An aluminum based surface, (i.e. a metal comprising aluminum or aluminum alloys, is first anodized in a sulfuric acid electrolyte of suitable strength. An electric current of suitable current density, comprising components of alternating current and direct current is used. The present invention includes the use of an incompletely rectified current. The current may be in a ratio such that the AC component is more than the DC component.

According to the present invention, the aluminum or its alloys is subjected to anodic oxidation in an aqueous solution comprising mainly sulfuric acid as the electrolyte, by using an electric current comprising both AC and DC components with the AC component being more than the DC component, then the resulting anodized film is dipped in a solution containing only metal salt without supplying electric current, and then sealed to obtain a colored aluminum.

An outstanding advantage in the present invention lies in the fact that the anodic oxidation is carried out by supplying electric current comprising both AC and DC components, in an electrolyte containing mainly sulfuric acid, and that in the coloring step the supply of electric current is not necessary as compared with the above discussed Asada method. This fact seems to be based on the following reason: The electric current comprising both AC and DC components, in which the AC component is greater, is supplied through the aqueous solution of sulfuric acid in the anodic oxidation, to form hydrogen sulfide in micropores of the anodized film by a reduction decomposition of sulfuric acid. Thus, when the anodized film containing hydrogen sulfide thus obtained is dipped in the metal salt solution, the hydrogen sulfide which is present in the micropores of said film is reacted with the metal ion to form a sulfide which is deposited thereon. The bond of hydrogen sulfide and metal ion is greatly enhanced by the heat of the sealing treatment, to produce strong and sharp colored film.

The current density value of the applied current depends upon the reaction conditions of the anodization step, such as for example, temperature, concentration of electrolyte, period of reaction, etc. Accordingly, no particular value is assigned to the current density. However, the component of direct current should not be so high as to make the coloring difficult, nor should the component of direct current be so low as to produce anodized surfaces or films which are soft. Similarly, in using unfiltered or incompletely rectified current, excessive direct current component would tend to make coloring difficult, but an insufficient amount of DC component would produce a soft surface.

A preferred range of values of AC and DC components may be specified by the ratio:

AC (effective Vtflllt) This ratio is satisfied in the below described Examples l-3.

The resulting anodized film or surface is then submersed or dipped into a single solution containing one or more metal salts.

Any type of metal salt, organic or inorganic, may be used in this invention. For example, such salts may be ferric ammonium oxalate, cobalt acetate, copper sulfate, cadmium sulfate, silver nitrate, nickel chloride and the like. The concentration of metal salts in the solution is preferably within the range of from 0.1 to 10 per. cent by weight (hereinafter being the same), with a range of from 0.5 to 2.0 percent being es ecially preferred.

The treated anodized surface is then subjected to a sealing treatment which may comprise the application of steam on to the surface for a period of time ranging from 30 to 60 minutes. This causes the color to come out and the surface to become sealed.

A better appreciation of the invention may be obtained by considering the following examples which are illustrative of the invention.

The density of the AC as used in the following Examples, and also as defined by Japanese industry, is defined to be:

Total alternating current Total surface area. of aluminum to be treat-ed This means that twice the Alternating Current having the above density is passed over each pole of aluminum as shown by the following formula:

EXAMPLE 1 tiugeurruut;

ninuui to ho truubvtl current having a current density of 1.2 X 2 Amp/dm and direct current having a current density of 0.8 Amp/dm The anodization was carried out at a temperature of about 20 C or room temperature, for about 70 minutes.

The samples having anodized surfaces were then treated under specific conditions listed in the below table 1, and with the following steps: (1) The anodized sample was washed with water, (2) Next, the sample was neutralized under a variety of conditions differing for each sample. (3) The neutralized sample was then again washed with water. (4) Next, the sample was dipped in a metal salt solution under a variety of condidried. (7) Thereafter, the sample was subjected to steam sealing to develop the color and to seal the surface.

containing about 170 g/l of H 50, and about 5 g./l. of A1, at a temperature of about from 18 to 20 C., for a period of about 40 minutes. The dipping treatment was carried out in 5 g./l. of cobalt acetate solution at a temperature of about 60 C. for

TABLE 1 Neutralization Dipping in metal salt Dipping Time time Color after Sample No. Kind of solution Temp. (min.) Kind of salt Dipping temp. min) seal 1 10% NI DOII Room temp. 1 2% fen'ie ammonium Xalnte Room 1011l[). Blank.

IINO: ...d0. 1 d0 .d0. 5 Do. Without neutralization" .do. 1 do 5 Black (reddish). 10% N114OII 1 2% CuSO; 5 Yellow green. 5 10% HNO3. 1 do 5 Green. 6 Without neu 1 do 5 o. 7 10% 1IN0 1 .do 10 C 5 Golden brown.

About C.

The sealing was obtained by subjecting the dipped surface I to high pressure steam of 3.5 l(g./cm. pressure, for about 30 minutes to perfect the coloring. 20 minutes. i

The above Table 1 reveals that various colors may be ob- As can be seen from Table 3, when the AC component in tained depending upon the kind of metal salt is employed. In the electric current supplied is decreased, the reduction of the testing for light resistance of class 8 is in the blue scale. Thus, sulfuric acid by the electric current is difficult and as a result, there were obtained high quality colored aluminum alloy sureven if the anodized film is dipped into the metal salt solution, faces. The thickness of the resulting colored film or coating the coloring compound can not be produced. However, when was about 28 microns. the AC component in the electric current to be supplied is increased, the sharp color may be obtained. EXAMPLE 2 What is claimed is:

A number of samples of aluminum alloys 25 were subjected Process, cglormg 1 Surface of an alummum based to anodization in a sulfuric acid electrolyte containing about 30 metal e i I l l 168 g/l of H 80, and 5.5 g./l. of A1, at a temperature of about mo l zmg ace an e ectro comammg i? y 20 C., for a period of time of about 60 minutes. The electric Sulfur: acid by Supplymg an elecmc current comPnsmg current which was used comprised a combination of alternatf and a DC component and havmg the ing current having a current density of 1.2 X 2 Amp/dm and o owmg a direct current com onent havin a current densit of 1.0 Amp/dm p g y AC Component (efiiectrve value) 1 i The anodized samples were then treated according to the DC Component steps outlined in Example 1, and under the conditions listed in the following Table 2. b. dipping the resulting anodized surface in a solution con TABLE 2 Neutralization Dipping in metal salt Dipping Time time Color after Sample N o. Kind of solution Temp. (min.) Kind of salt Dipping temp. (min seal 1 1.0% N110; Room temp... 1 2% CuSOi Room temp 5 Green. 2 do d0. 1 2% ferric ammouiumo .do 5 Black. 3"... 0 "do.-. 1 1% CoSO4.. Jim 5 Gray. -i 3% Nil/2C0: "(10... 1 .rl0 5 Black. 5 10% HNOa .d0 1 .do. 5 Pale era 10% NILOH d0 1 .tl0 5 Melon.

10% HNO "J10. 1 rlo, 5 Hold. 3% NmCO; ..d0 1 do 5 Deep gold. 10% HNOa d0 1 tlo 5 Iale gray. 10%N1I O1 ...do 1 o 1 .110. 5 lale blo -k. 10% NHiOH d0 1 1% CO(CII3COO) (3.. 5 Bla k. 12.. 10% IINO; do 1 1% Pb(CH COO)g 60 C 5 Brown.

about 2 minutes. The sealing treatment of said dipped surface was carried out at 3.5 kg/cmpressure of steam for about 30 When each of the foregoing examples were tested for corroa sion resistance and abrasion resistance according to MS (Japanese Industrial Standard) 11-8601, the results were found to be, for corrosion resistance about from 200 to 1,300 sec., and for abrasion resistance about from 2,500 to 3,500 sec.

EXAMPLE 3 shown in the following Table 3, in a sulfuric acid electrolyte 70 taining at least one metal salt, the concentration of said metal salt in said solution being within the range of from 0.1 percent by weight to 10 percent by weight; and

c. subjecting the dipped anodized surface to high pressure of about 3.5 Kg/cm of steam for a period of from 30 minutes to 60 minutes, whereby coloring is produced and said surface is sealed.

2. Process according to claim 1, wherein said solution comprises a combination of metal salts selected from the group consisting of (1) copper acetate-nickel chloride, (2) nickel chloride-zinc chloride, and (3) cobalt acetate-copper sulfate.

3 Process for coloring the surface of an aluminum based metal comprising the steps of a. anodizing said surface in an electrolyte containing mainly sulfuric acid by supplying an electric current comprising TABLE 3 Sample Number .l l 2 3 4 5 Electric current (amp/dram):

AC .1 0.5X2 0.6X2 0.7)(2 1 0.8)(2 0..1X2. DC ..1.2 1.2 1.2 1.2 1.2. Color altersealim. Colorless Very slight brownM" sli ht brown lale brown .1 Middle brown.

Nora-A0 component in the above Sample 1 is deviated from the specified range. of the. present invention.

an AC component and a DC component and having the following ratio:

DC Component b. dipping the resulting anodized surface in a solution containing a combination of metal salts selected from the group consisting of (1) copper acetate-nickel chloride, (2) nickel chloride-zinc chloride, and (3) cobalt acetatecopper sulfate, the concentration of said metal salts in 

2. Process according to claim 1, wherein said solution comprises a combination of metal salts selected from the group consisting of (1) copper acetate-nickel chloride, (2) nickel chloride-zinc chloride, and (3) cobalt acetate-copper sulfate.
 3. Process for coloring the surface of an aluminum based metal comprising the steps of a. anodizing said surface in an electrolyte containing mainly sulfuric acid by supplying an electric current comprising an AC component and a DC component and having the following ratio: b. dipping the resulting anodized surface in a solution containing a combination of metal salts selected from the group consisting of (1) copper acetate-nickel chloride, (2) nickel chloride-zinc chloride, and (3) cobalt acetate-copper sulfate, the concentration of said metal salts in said solution being within the range of from 0.1 percent by weight to 10 percent by weight; and c. sealing the dipped anodized surface to produce coloring thereof.
 4. Process according to claim 3, wherein said treating step comprises subjecting the dipped anodized surface to high pressure of about 3.5 Kg./cm.2 or more of steam for a period of from 30 minutes to 60 minutes, whereby said coloring is produced and said surface is sealed. 